Damascene process using cleaning solution

ABSTRACT

A cleaning solution is provided. The cleaning solution includes a fluorine containing compound, an inorganic acid, a chelating agent containing a carboxylic group and water for balance. The content of the fluorine containing compound is 0.01-0.5 wt % of. The content of the inorganic acid is 1-5 wt %.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation application of an application Ser. No.12/830,566, filed Jul. 6, 2010. The entirety of the above-mentionedpatent are hereby incorporated by reference herein and made a part ofthis specification.

FIELD OF THE INVENTION

The present invention relates to a cleaning solution and a damasceneprocess using the same.

BACKGROUND OF THE INVENTION

A Dual damascene process is a technology widely applied in asemiconductor process. To reduce the RC delay caused by a parasiticcapacitance, the current dual damascene process adopts an ultra low-k(ULK) material as a dielectric layer. Further, with the minimization ofthe device, a titanium nitride (TiN) hard mask layer is formed on thedielectric layer, and then the required patterns are preciselytransferred to the dielectric layer by utilizing different etchingselectivities of the TiN hard mask layer and the dielectric layer.

The pattern transfer is usually achieved by a dry etching process.However, during the etching process, the reactive gases passing into areaction chamber may also undergo a polymerization reaction. Therefore,the organic polymer formed from the polymerization reaction is depositedon the surface of the device. Moreover, the reactive gases used foretching the dielectric layer are mostly fluorine-containing gases. Thesefluorine-containing gases may react with the TiN hard mask layer toproduce titanium fluoride (TiFx) on the surface of the device, and thus,a profile change of the device, abnormal conduction, leakage or shortcircuiting between film layers is caused, and the reliability of thedevice is accordingly reduced.

The effect produced by the polymer and titanium fluoride residues isparticularly significant in the deep sub-micro fabrication process.Further, upon the study, the post-etch cleaning process may effect theconduction ability of the device by etching the exposed metal linesbelow the dual damascene opening, cause a profile change by swelling thedielectric layer with the cleaning solution, or lead to an increase inthe dielectric constant. Therefore, the post-etch cleaning process hasbecome a very important step in the duel damascene process.

SUMMARY OF THE INVENTION

The present invention provides a cleaning solution to effectively removethe residues containing a plurality of species.

The present further invention provides a damascene process to reduce thesurface damage (copper loss) of the conductive layer, avoid damages ofthe dielectric layer or an increase in the dielectric constant, orprevent bridges between the dual damascene structures, and thus, thereliability of the semiconductor device is enhanced.

The present invention provides a cleaning solution including a fluorinecontaining compound, an inorganic acid, a chelating agent containing acarboxylic group and water for balance. The content of the fluorinecontaining compound is 0.01-0.5 wt % of. The content of the inorganicacid is 1-5 wt %.

According to an embodiment of the present invention, the inorganic acidincludes sulfuric acid (H₂SO₄) or hydrochloric acid (HCl).

According to an embodiment of the present invention, the chelating agentcontaining the carboxylic group includes oxalic acid.

According to an embodiment of the present invention, the cleaningsolution consists of 0.01-0.5 wt % of the fluorine containing compound;1-5 wt % of the inorganic acid; the chelating agent containing thecarboxylic group; and water for balance.

According to an embodiment of the present invention, the fluorinecontaining compound includes hydrofluoric acid (HF) and ammoniumfluoride (NH₄F).

According to an embodiment of the present invention, the cleaningsolution further includes ethylenediaminetetraacetic acid (EDTA).

According to an embodiment of the present invention, the cleaningsolution further includes triethanolamine (TEA).

The present invention further provides a damascene process. The processincludes the following steps. A substrate having a conductive layerthereon is provided. A dielectric layer and a metal hard mask layer issequentially formed on the substrate. The metal hard mask layer and thedielectric layer are sequentially etched so as to form an openingexposing the conductive layer. A post-etch cleaning process with acleaning solution performed. The cleaning solution includes 0.01-0.5 wt% of a fluorine containing compound; 1-5 wt % of an inorganic acid; achelating agent containing a carboxylic group; and water for balance.

According to an embodiment of the present invention, the inorganic acidincludes sulfuric acid (H₂SO₄) or hydrochloric acid (HCl).

According to an embodiment of the present invention, the chelating agentcontaining the carboxylic group includes oxalic acid.

According to an embodiment of the present invention, the cleaningsolution consists of 0.01-0.5 wt % of the fluorine containing compound;1-5 wt % of the inorganic acid; the chelating agent containing thecarboxylic group; and water for balance.

According to an embodiment of the present invention, the openingincludes a dual damascene opening, a via opening or a contact opening.

According to an embodiment of the present invention, the metal hard masklayer includes titanium, titanium nitride, tantalum, tantalum nitride,tungsten, tungsten nitride, or a combination thereof.

According to an embodiment of the present invention, the damasceneprocess further includes the step of forming a buffer layer afterforming the dielectric layer and before the step of forming the metalhard mask layer and forming a cap layer after the step of forming themetal hard mask layer, wherein the cap layer includes silicon carbide,silicon nitride or silicon oxynitride.

According to an embodiment of the present invention, the buffer layerincludes silicon oxide or silicon oxynitride.

According to an embodiment of the present invention, the fluorinecontaining compound includes hydrofluoric acid (HF) and ammoniumfluoride (NH₄F).

According to an embodiment of the present invention, hydrofluoric acid(HF) is 0.01-0.1 wt %.

According to an embodiment of the present invention, ammonium fluoride(NH₄F) is 0.05-0.5 wt %.

According to an embodiment of the present invention, the cleaningsolution further includes ethylenediaminetetraacetic acid (EDTA).

According to an embodiment of the present invention, the cleaningsolution further includes triethanolamine (TEA).

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more readily apparent to thoseordinarily skilled in the art after reviewing the following detaileddescription and accompanying drawings, in which:

FIGS. 1A to 1E schematically illustrate cross-sectional views of adamascene process according to an embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention will now be described more specifically withreference to the following embodiments. It is to be noted that thefollowing descriptions of preferred embodiments of this invention arepresented herein for purpose of illustration and description only. It isnot intended to be exhaustive or to be limited to the precise formdisclosed.

An embodiment of the present invention provides a cleaning solution. Thecleaning solution includes hydrofluoric acid (HF), an inorganic acid,ammonium fluoride (NH₄F), a chelating agent containing a carboxylicgroup, triethanolamine (TEA), ethylenediaminetetraacetic acid (EDTA) andwater.

In the cleaning solution, the content of hydrofluoric acid is 0.01-0.1wt %. The content of the strong acid is 1-5 wt %. The strong acid is aninorganic acid with pKa value less than −1.74, such as sulfuric acid(H₂SO₄) or hydrochloric acid (HCl). The content of ammonium fluoride is0.05-0.5 wt %. The chelating agent containing the carboxylic groupincludes oxalic acid, for example. The rest of the cleaning solution iswater. The water is de-ionized (DI) water. In an embodiment, thecleaning solution consists of hydrofluoric acid, the strong acid,ammonium fluoride, the chelating agent containing the carboxylic group,triethanolamine, ethylenediaminetetraacetic acid and water, and othercomponents are not included.

The cleaning solution can be applied to a damascene process. A dualdamascene process is taken as an example in the following.

FIGS. 1A to 1E schematically illustrate cross-sectional views of adamascene process according to an embodiment of the present invention.

Referring to FIG. 1A, a substrate 10 having a conductive layer 20 and acap layer 30 sequentially thereon is provided. The conductive layer 20includes Cu, CuAl alloy or CuAlSi alloy, for example. The cap layer 30includes silicon nitride, silicon oxynitirde or silicon carbide, forexample. Thereafter, a dielectric layer 40, a buffer layer 50, a metalhard mask layer 60, and a cap layer 65 are sequentially formed on thecap layer 30. The dielectric layer 40 includes an ultra low-k (ULK)material, for example. The ultra low-k material is a material with adielectric constant of 2.5˜2.7 or lower. The ultra low-k materialincludes Black diamond (Trademark of AMAT), or Dense ULK (Trademark ofNOVELLUS) for example. The material of the buffer layer 50 is differentfrom that of the dielectric layer 40. The buffer layer 50 includessilicon oxide or silicon oxynitride, for example. The metal hard masklayer 60 includes metal or metal nitride, such as titanium, titaniumnitride, tantalum, tantalum nitride, tungsten, tungsten nitride, or acombination thereof. The cap layer 65 is adapted to protect the metalhard mask layer 60 and includes silicon nitride, silicon oxide, siliconoxynitirde or silicon carbide, for example.

Referring to FIG. 1B, a dual damascene opening 70 is formed in the caplayer 65, the metal hard mask layer 60, the buffer layer 50, thedielectric layer 40 and the cap layer 30 by photolithography and etchingprocesses. The bottom of the dual damascene opening 70 exposes theconductive layer 20. The dual damascene opening 70 is formed by alaterally extending trench 72 disposed at an upper position and avertically extending via opening 74 disposed at a lower position. Themethod of forming the dual damascene opening 70 includes forming the viaopening 74 prior to the trench 72, or forming the trench 72 prior to thevia opening 74. The etching gases for the etching process usuallyinclude fluorine, so as to remove the metal such as refractory metal inthe metal hard mask layer 60. During the etching process, polymer isusually formed on the sidewall of the dual damascene opening 70.Moreover, in the etching process, the copper loss problem occurs due tothe formation of copper oxide (CuO_(x)) or CuO_(x)F_(y) on the surfaceof the conductive layer 20 (e.g. copper layer) exposed by the dualdamascene opening 70. Therefore, after the step of forming the dualdamascene opening 70, the to-be-removed residual species includerefractory metal, fluorine, oxygen, silicon, carbon and copper.

Referring to FIG. 1C, a chemical cleaning process 80 (or a post-etchcleaning process) is performed with the above-mentioned cleaningsolution, so as to remove the residues on the substrate 10 as well asthe damaged surface of the conductive layer 20. The cleaning solutionconsists of hydrofluoric acid, the strong acid, ammonium fluoride, thechelating agent containing the carboxylic group, triethanolamine,ethylenediaminetetraacetic acid and water, and other components are notincluded. The components and contents in the cleaning solution aredescribed above, and the details are not iterated herein. The chemicalcleaning process 80 can be performed at room temperature, such as 20 to50° C., for example. The time period of the chemical cleaning process 80is 60 to 120 seconds, for example.

Hydrofluoric acid, sulfuric acid and ammonium fluoride in the cleaningsolution are configured for providing fluorine ions and adjusting the pHvalue. The chelating agent containing the carboxylic group,triethanolamine and ethylenediaminetetraacetic acid in the cleaningsolution serve as a chelating agent, resolve the metal complexes in theaqueous solution, and stabilize the surface of the conductive layer toavoid re-oxidation of the conductive layer, and thus, they are regardedas a surface oxidation inhibitor.

In details, sulfuric acid in the cleaning solution hardly reacts withthe dielectric layer 40, so that damages of the dielectric layer 40 donot occur. However, sulfuric acid can react with CuO_(x) or CuO_(x)F_(y)on the surface of the conductive layer 20 to form water-soluble copperions (Cu²⁺). The copper ions can chelate with the chelating agentcontaining the carboxylic group, so as to avoid copper loss caused byre-oxidation of the conductive layer 20. Further, sulfuric acid,hydrofluoric acid and ammonium fluoride in the cleaning solution aremixed to form SO₃F⁻, which is a strong nucleophilic reagent to make theCu⁻R bonds break and achieve the purpose of removing the residues.

Referring to FIG. 1D, a cleaning process 90 is performed after the stepof performing the chemical cleaning process 80. In an embodiment, thecleaning process 90 is performed immediately after the step ofperforming the chemical cleaning process 80, and no other processesbetween the cleaning process 90 and the chemical cleaning process 80 arepresent. The cleaning process 90 is performed with DI water only, and noother components are used. The cleaning process 90 can be performed atroom temperature, such as 20 to 30° C., for example. The time period ofthe cleaning process 90 is 30 to 90 seconds, for example. Thereafter, abaking process is performed. The temperature of the baking process is200 to 300° C., and the time period of the same is 30 to 60 minutes, forexample.

Referring to FIG. 1E, a conductive material (not shown) is formed on thecap layer 65 and the metal hard mask layer 60 filling in the dualdamascene opening 70. The conductive material includes copper, forexample. Thereafter, a chemical mechanical polishing (CMP) or an etchingback process is performed to remove the conductive material on the caplayer 65 and remain the conductive material 100 in the dual damasceneopening 70. Afterwards, the cap layer 65, the metal hard mask layer 60,and the buffer layer 50 are removed.

The dual damascene process in the above-mentioned embodiment is providedfor illustration purposes, and is not construed as limiting the presentinvention. The above-mentioned dual damascene opening can also be a viaopening or a contact opening only. Therefore, the above-mentionedcleaning solution can be applied to a single damascene process.

Further, the cleaning solution is not limited to apply to a damasceneprocess. The cleaning solution of the present invention can be appliedto a semiconductor process with to-be-removed residual species includingrefractory metal, fluorine, oxygen, silicon, carbon and copper.

EXAMPLE

An ultra low-k dielectric layer, a silicon oxynitride layer and atitanium nitride layer are sequentially formed on a substrate having acopper layer and a carbide silicon nitride layer thereon. Thereafter, aphotolithography process is performed and followed by a dry etchingprocess with fluorine containing gases, so as to form a dual damasceneopening. Afterwards, a chemical cleaning process is performed with acleaning solution (0.06 wt % of hydrofluoric acid, 3 wt % of sulfuricacid, 0.1 wt % of ammonia fluoride, 10 wt % of oxalic acid, 10 wt % ofTEA, 0.2 wt % of EDTA and water for balance), and then another cleaningprocess is performed immediately with DI water.

The result shows that the residues in the process can be effectivelyremoved by performing the chemical cleaning process with the cleaningsolution and followed by another cleaning process with DI water.Moreover, damages are not found on the surface of the dielectric layeror the copper layer, or an increase in the dielectric constant is notcaused. Bridges are not observed between the formed dual damascenestructures. Thus, the reliability of the semiconductor device can beaccordingly enhanced.

Comparative Examples 1 to 6

A dual damascene opening is formed by the method of the above-mentionedExample. Thereafter, a post-etch cleaning process is performed withdifferent cleaning solutions including different components, andimmediately followed by another cleaning process with DI water. Theresults are shown in Table 1.

TABLE 1 Components of cleaning solution Results Comparative 10 wt % ofoxalic acid, 0.1 wt % of Copper surface example 1 ammonia fluoride, 3 wt% of damage sulfuric acid, 0.06 wt % of hydrofluoric acid and water forbalance Comparative 10 wt % citric acid, 0.1 wt % of Polymer residueexample 2 ammonia fluoride, 3 wt % of sulfuric acid, 0.06 wt % ofhydrofluoric acid and water for balance Comparative 5 wt % ofiminodiacetic acid (IDA), Polymer residue example 3 0.1 wt % of ammoniafluoride, Dielectric layer 3 wt % of sulfuric acid, 0.06 wt % of damagehydrofluoric acid and water for balance Comparative 10 wt % of oxalicacid, 0.2 wt % of Copper surface example 4 EDTA, 3 wt % of sulfuricacid, damage Polymer 0.06 wt % of hydrofluoric acid and residue waterfor balance Comparative 10 wt % of TEA, 0.1 wt % of Copper surfaceexample 5 ammonia fluoride, 3 wt % of damage sulfuric acid, 0.06 wt % ofhydrofluoric acid and water for balance Comparative 5 wt % ofiminodiacetic acid, 1 wt % Dielectric layer example 6 of NH₄HF₂, 3 wt %of sulfuric acid, damage Copper 0.06 wt % of hydrofluoric acid andsurface damage water for balance

While the invention has been described in terms of what is presentlyconsidered to be the most practical and preferred embodiments, it is tobe understood that the invention needs not be limited to the disclosedembodiment. On the contrary, it is intended to cover variousmodifications and similar arrangements included within the spirit andscope of the appended claims which are to be accorded with the broadestinterpretation so as to encompass all such modifications and similarstructures.

What is claimed is:
 1. A damascene process, comprising: providing asubstrate having a conductive layer thereon; sequentially forming adielectric layer and a metal hard mask layer on the substrate;sequentially etching the metal hard mask layer and the dielectric layer,so as to form an opening exposing the conductive layer; and performing apost-etch cleaning process with a cleaning solution, wherein thecleaning solution comprises: (a) 0.01-0.5 wt % of a fluorine containingcompound; (b) 1-5 wt % of an inorganic acid; (c) a chelating agentcontaining a carboxylic group; (d) water for balance; and (e)ethylenediaminetetraacetic acid (EDTA).
 2. The damascene process ofclaim 1, wherein the inorganic acid comprises sulfuric acid (H₂SO₄) orhydrochloric acid (HCI).
 3. The damascene process of claim 1, whereinthe chelating agent comprises oxalic acid.
 4. The damascene process ofclaim 1, wherein the opening comprises a dual damascene opening, a viaopening or a contact opening.
 5. The damascene process of claim 1,wherein the metal hard mask layer comprises titanium, titanium nitride,tantalum, tantalum nitride, tungsten, tungsten nitride, or a combinationthereof.
 6. The damascene process of claim 1, further comprising forminga buffer layer after the steps of forming the dielectric layer andbefore the step of forming the metal hard mask layer and forming a caplayer after the step of forming the metal hard mask layer, wherein thecap layer comprises silicon carbide, silicon nitride or siliconoxynitride.
 7. The damascene process of claim 6, wherein the bufferlayer comprises silicon oxide or silicon oxynitride.
 8. The damasceneprocess of claim 1, wherein the fluorine containing compound compriseshydrofluoric acid (HF) and ammonium fluoride (NH₄F).
 9. The damasceneprocess of claim 8, wherein the hydrofluoric acid (HF) is 0.01-0.1 wt %.10. The damascene process of claim 8, wherein the ammonium fluoride(NH₄F) is 0.05-0.5 wt %.
 11. The damascene process of claim 1, whereinthe cleaning solution further comprises (f) triethanolamine (TEA).